Re: st: sampling weight in --sum,--fsum

[Steven Samuels <sjhsamuels@earthlink.net>]

Mandy, To answer your questions, you need to distinguish two kinds of  
description:

a. Of the sample itself
b. Of the population that the sample is supposed to represent.


a. For describing the sample itself, use the basic Stata commands  
like -sum- -tab- without weights.  This is important--readers will  
want to know the composition of the sample, for example, were the  
sample sizes in important subgroups big enough to give reliable results?

b. Describe the population?  For many populations, you would not do  
"basic description".  For example, if the population is the US or a  
State, most characteristics about it are known from other sources.   
The survey weights may even have been adjusted to reproduce what is  
known about the population--its age and gender distribution, for  
example.  On the other hand, if the population is unique, not known  
from other sources, then description might be the point of the  
survey.  For example, you might have a sample of a district in a  
city.  To describe the population you would use -svy- commands, not  
ordinary Stata commands, as Joao stated in his email.


To expand on Joao's answer to your second question:  With weights,  
but without the cluster and stratum identifications, regressions with  
the -svy- prefix can give good point estimates, but tests, p-values,  
standard errors and confidence intervals will all be wrong. Usually  
the reported SE's will be smaller than the actual SE's and the  
reported p-values will be "too significant".

-Steven


On Sep 9, 2008, at 10:39 AM, Man Jia wrote:


> Hi everyone,
>
> I have a simple question about survey data. I'd like to report the
> basic statistic description for a survey data set. But the commands
> like --sum --fsum can't use the option of pweight (probability  
> weight).
> What can be used is either fweigtht or aweight.
>
> Could anyone help me with the following questions?
>
> 1) How should I get the basic statistics for a survey data which the
> sampling weight is known?
>
> 2) Now I have no information of strata or cluster. What I only know is
> the sampling weight assigned to each individual. When I just use
> pweight to do OLS regressions with svy command, should the
> missing-strata--and--cluster problem be a concern ?
>
> Thanks for your help!
>
> Mandy
>
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